Electron discharge device



Oct. 4, 1960 c. E. WARD ELECTRON DISCHARGE DEVICE Filed May 26, 1958INVENTORQ Curtis E. Ward Attorney United States Patent ELECTRONDISCHARGE DEVICE Curtis E. Ward, Los Altos, Califl, assignor to VarianAssociates, Palo Alto, Calif a corporation of Califomia Filed May 26,1958, Ser. No. 737,734

11 Claims. (Cl. 315-5.21)

This invention relates in general to high frequency devices and moreparticularly to a novel improved velocity modulation device of thetunable external cavity resonator type.

The particular type of klystron to which the present invention relatesis an internal-external cavity resonator type klystron in which thekylstron frequency is tuned by means of a tuning mechanism in a cavityresonator outside the vacuum envelope of the device, this externalcavity resonator being heavily coupled through an iris coupling and awave energy permeable vacuum seal or window to an internal cavityresonator within the evacuated portion of the klystron. Heretofore lossymembers such as screws have been inserted into the external cavityresonator at desired points to eliminate undesired modes of operation ofthe klystron. The present invention has for its object the provision ofa novel internal-external cavity resonator type klystron having animproved window coupling structure and an improved mode suppressorarrangement incorporated in the external cavity resonator portion of theklystron.

One feature of the present invention is the provision of a klystrondevice of the internal-external cavity resonator type having an improvedwindow coupling structure.

Another feature of the present invention is the provision of a klystronof the internal-external cavity resonator type which incorporates anovel waveguide mode suppressor trap in the external cavity resonatorfor suppressing undesired modes.

Another feature of the present invention is the provision of a novelklystron of the above featured type wherein the operation of the modesuppressor waveguide trap .is enhanced by means of a coupling member ormode handle which also serves as an iris or window loading member forthe klystron.

These and other features and advantages of the present invention willbecome more apparent upon a perusal of the following specification takenin connection with the drawings, wherein,

Fig. 1 is an elevation View partly cutaway and partly in longitudinalsection of a reflex klystron device which embodies the novel modesuppressor mechanism in the external cavity,

Fig. 2 is a cross section view of the klystron of Fig. 1 taken alongsection lines 22,

Fig. 3 is a longitudinal cross section view of an external cavityresonator portion of a reflex klystron which incor porates a secondembodiment of the present invention, and

Fig. 4 is a cross section view of the structure shown in Fig. 3 takenalong the section line 44 therein.

Referring now to Figs. 1 and 2 there is shown a reflex klystron in whichthe present invention is incorporated for purposes of illustration, thereflex klystron comprising a metallic main body block 11, as of steel,having a cylindrical bore therein in which a metallic reflector bulb 12and cathode bulb 13 as of, for example, steel are brazed. A reflectorbutton 14 as of nickel is mounted on and extends within the reflectorbulb 12. A steel reflector header Patented Oct. 4, 19 60 15 is brazed onthe inner end of the reflector bulb 12 and a copper resonator grid 16 isbrazed on the header 15. A copper anode header 17 is brazed Within themain body 11 and carries a second copper resonator grid 18 which cooperates with grid 16 to form an interaction gap in the internal cavityresonator of the klystron. A cathode button 19 and associated focusingmember 21 are mounted within the cathode bulb 13.

A window plate 21, as of steel, is brazed to the main body 11, thewindow plate having an oval-shaped flexible Window frame 22, as ofKovar, vacuum sealed therein. An oval shaped Wave permeable ceramicwindow 23' is vacuum sealed in the frame. The window frame 22 is coupledto the main body 11 by means of thin metallic conducting straps 24, asof nickel, which serve as window shorts as described below. An externalcavity resonator member 25 is secured to a metallic cavity cup 26 whichin turn is secured as by brazing on the window plate 21, the rim of thecavity cup 26 being pressed down over the back of the window plate 21.An iris plate 27, which has a circular opening therein, and a waveguideflange 28 are fixed to the outer end of the external cavity resonatormember 25. A capacitive tuning post 29 is mounted on the external cavityresonator and adapted to be screwed therein for selectively tuning thefrequency of this reflex klystron. A tuning member of this type is shownand described in US. patent application Serial No. 675,491, filed July31, 1957, by B. C. Gardner et al.

In operation, electrons emitted from the cathode 19 are focused into abeam by the focusing electrode 21 and accelerated through the klystronby high positive potential on the accelerator electrode 17. Inaccordance with wellknown reflex klystron action, electrons pass throughthe resonator gap between grids 18 and 16 where they interact with theR.F. electric field across the gap, the R.F. field velocity-modulatingthe beam. Electrons pass into the space adjacent the reflector electrode14 which carries a negative potential adapted to repel the electrons inthe beam. The electrons are turned about and again passed through theresonator gap between grids 16 and 18 in bunches due to the velocitymodulation effect which took place in the electron beam. The bunchedelectrons deliver energy to the field across the resonator gap, the R.F.energy being removed from the cavity resonator through the window 23into the external cavity resonator. The klystron may be tuned over itsoperating frequency range by means of the tuner rod 29 in the externalcavity resonator. The radio frequency energy passes from the externalcavity resonator through the opening in iris plate 27 to the externalload circuits.

The window 23 is mounted in the thin flexible oval frame 22 which inturn is mounted on its outer flange in the window plate 21 for thepurpose of allowing a definite amount of flexibility to the vacuumsealed window of this klystron. This flexibility is needed due to themechanical stresses and strains of mounting, vibration, etc. to whichthe Window is subjected during use of the klystron and also because ofthe expansion and contractions due to temperature variations and thelike. Without the flexibiltiy provided by this window frame 22, thevacuum sealed window has a tendency to crack or open at its seal withthe result that the klystron loses its vaccurn. The window is preferablyoval shaped because of the better tuning range obtained in the externalcavity resonator with the movable tuner post 29. The result of the ovalshape to the window frame and the particular mounting arrangement of theflexible Window frame in the window plate 21 is that a series inductiveelement or choke is formed in the space 22' between the main body 11,the window frame 22, and window plate 21. It has been found that theeffects due to this series inductive element or choke formed between thewindow and the body may be eliminated by means of flexible metallicstrips 24 brazed between the body 11 and the window frame 22. Thus'theadvantages of a flexibly mounted-window as shown may be obtained withoutthe resultant deleterious effect of achoke being evident. It has beenfound that one strip across each of the topand bottom sides of theWindow as shown in Pig. 1, works very well. A total of four strips inone embodiment resulted in a slight improvement over two strips.

A. mode s ppressor of novel construction is incorporated in the tunableexternal cavity resonator for suppressing undesired modes of operationof the reflex klys-tron. For example, in one embodiment of thisinvention the 3/2 mode is suppressed, the klystron operating-inthe fullwave mode. This mode suppressor includes a wave trap cup 32 coupled tothe external cavity 4 resonator type comprising a main body portionhaving an evacuated resonator type comprising a main body portion havingan evacuated cavity resonator fonned therein, another body portionhaving an unevacuated external cavity resonator formed therein, a waveenergy permeable window vacuum sealed between the internal cavityresonator and theexternal cavity resonator, the external cavityresonator being heavily coupled electrically to said internal cavityresonator through said window, a tuner mechanism in said externalcavity'resonator over its operating frequency range for tuning said reflexklystron,

, means forsuppressing undesired modes of operation of resonator throughan opening 31 in the lower wall of theexternal cavity resonator. Thiswave trap cup is formed from a sheet of metal such as nickel folded intoa box-like cup which issccured as by spot-welding to the external cavityresonator 25 and to a block 33 which has been brazed to the waveguideflange .28. The sides 34 of this wave trap have slots 34' therein and,in' addition, small indented lips 35 are located in the longer side ofthe wave trap which accommodate a lossy resistive card 36. This card isfixedly secured within the wave trap by tightly closing the edges of theslots 34 on the ends of the card 36 during spot welding of the cup 32 tothe klystron. The. opening 31 through the external resonator wall isapproximately .4m long and the distance between the resistor card 36 andthe end of the cup is also approximately AA. A U-shaped mode handle 37as of nickel is secured within the external cavity resonator and servesa dual purpose. It serves as a window loading member for optimizing thecoupling through window 23 between the internal and external cavityresonators and, in addition, it serves to give a wider frequencyseparation between the desired mode of operation of this klystron andthe undesired mode which the mode suppressor 32 is arranged to suppress,thereby enhancing the suppression of the undesired mode. For example, inone .klystron made in accordance with this invention thefrequencyseparation was improved by about 50% due to utilization of the modehandle of proper width, i.e. horizontal length as viewed in Fig. 1. Theoptimum width of the mode handle .is determined mainly on a trial anderror basis to accomplish the optimum frequency separation. The U-shaped configuration of the. mode. handle permitsslight verticaldisplacement of this mode handle by means of a bending tool insertedthrough the opening in iris plate 27., thus allowing for slightadjustments of the Window loading and the mode suppressingcharacteristics of the mode handle.

Another form of the mode suppressor wherein two cuplike members areutilized is shown in Figs. 3 and 4 which depicts only the externalcavity resonator portion of a 'k'lystron with the tuning screw removed.The internal cup 38 is spot-welded to the external cavity resonator 39over the coupling opening 41. The horizontal length of this cup is AM.The external cup 42 is also spot-welded to the external cavity resonatorand the waveguide flange, a. resistor card 43 being securely :heldwithin this cup, approximately 11 from the waveguide flange, bysqueezing the sides of the cup on the card during spot-welding. 'Thetwo. cups form a sinuous wave energy path of the desired wave lengthbetween the external cavity resonator andthe resistor card.

.Since many changes could be made .in the above const-ruction and manyapparently widely difierent embodiments of this invention could be madewithout. departing from the scope thereof, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and notin :a limitingsense.

What is claimed is:

1. A reflex klystron of the internal-external cavity said reflex'klystron comprising 'a wave trap coupled to said external cavityresonator through an'opening in the wall of said external cavityresonator, said wave trap comprising a waveguide and having a waveenergy absorbing member therein for absorbing the energy of saidundesired mode, the electrical length of said wave trap being ofsufficient dimension to suppress the undesired mode, and ametallicconducting member in said external cavity resonator adjacent said wavepermeable window for producing optimum wave energy coupling between saidinternal and said external cavity resonator and positioned in saidexternal cavity resonator for also optimizing the frequency separationbetween the undesired mode 'to be suppressed and the desired mode ofoperation of the reflex klystron.

2. A reflex klystron device as claimed in claim 1 wherein the wall ofsaid external cavity resonator in which the coupling opening leading tothe wave trap is located is at least one-quarter wave length thick.

3. A reflex klystron device as claimed in claim 1 wherein said waveenergy absorbing member comprises a resistive card and wherein said wavetrap comprises a sheet of metal folded on at least three sides to form abox-like structure, two of the sides having slots therein adapted toaccommodate and grip the ends of the resistive card to thereby hold thecard within the wave trap.

4. A reflex klystron device as claimed in claim 1 wherein saidconducting member utilized for enhancing the coupling between, theinternal cavity resonator and the external cavity resonator and forseparating the modes of operation of thereflex klystron comprises aU-shaped conducting member mounted at its ends in the external cavityresonator and extending adjacent the vacuum seal window between theinternal and external cavity reso nators.

'5. A reflex klystron as claimed. in claim '1 wherein said wave trapcomprises two sheets of metal folded to form a pair of box-likestructures, one of said structures being mounted on said klystron overthe opening in the wall of said external cavity resonator and the secondof said structures being mounted over said one structure whereby asinuous 'wave energy path is produced through said two wave'trapstructures, said wave energy absorbing member being positioned in saidsecond structure.

96. A reflex klystron as claimed in claim 5 wherein said wave energyabsorbing member comprises a resistive card.

7. .A reflex 'klystron as claimed in claim 6 wherein said resistive cardis received in slots in the sides of said second structure.

8. A reflex klystron of the internal-external cavity resonator typecomprising a .main body portion in which the internal cavity resonatoris formed, a window plate portion integral with said body portion havinga substantially oval-shaped opening therein, a flexible oval-shapedwindow frame having an oval-shaped wave energy permeable material vacuumsealed therein, the window frame being vacuum sealed in the opening inthe window plate whereby a series inductive element or choke space isformed between the flexible window frame and said body and window plateportions, and plurality of conductive flexible strips securedbetween-said flexible window frame and the main body portion to serve aschoke shorts.

9. A reflex klystron of the internal-external cavity resonator typecomprising a main body portion having an evacuated cavity resonatorformed therein, a window plate portion integral with said body portionhaving a substantially oval-shaped opening therein, a flexibleovalshaped window frame having an oval-shaped wave energy permeablematerial vacuum sealed therein, the window frame being vacuum sealed inthe opening in the window plate whereby a series inductive element orchoke space is formed between the flexible window frame and said bodyand window plate portions, a plurality of conductive flexible stripssecured between said flexible window frame and the main body portionto'serve as choke shorts, another body portion having an external cavityresonator formed therein and mounted over said window, a tuner mechanismin said external cavity resonator for tuning said reflex klystron, meansfor suppressing undesired modes of operation of said reflex klystroncomprising a wave trap coupled to said external cavity resonator throughan opening in the wall of said external cavity resonator, said wave traphaving a wave energy absorbing member therein for absorbing the energyof said undesired mode, the electrical length of said wave trap being ofsuflicient dimension to suppress the undesired mode, and a metallicconducting member in said external cavity resonator adjacent said wavepermeable window for producing optimum wave energy coupling between saidinternal and said external cavity resonator and positioned in saidexternal cavity resonator for also optimizing the frequency separationbetween the undesired mode to be suppressed and the desired mode ofoperation of the reflex klystron.

10. A reflex klystron comprising a main body in which an evacuatedcavity resonator is formed, said main body having a substantiallyoval-shaped opening therein leading to the cavity resonator, a flexibleoval-shaped window frame having an oval-shaped wave energy permeablematerial vacuum sealed therein, the window frame being vacuum sealed inthe opening in said body whereby a series inductive element or chokespace is formed between the flexible window frame and said body, and aplurality of conductive flexible strips secured between said flexiblewindow frame and the main body to serve as choke shorts.

11. A reflex klystron of the internal-external cavity resonator typecomprising a main body portion having an evacuated cavity resonatorformed therein, a window plate portion integral with said body portionhaving a substantially oval-shaped opening therein, a flexibleovalshaped window frame having an oval-shaped wave energy permeablematerial vacuum sealed therein, the window frame being vacuum sealed inthe opening in the window plate whereby a series inductive element orchoke space is formed between the flexible window frame and said bodyand window plate portions, a plurality of conductive flexible stripssecured between said flexible window frame and the main body portion toserve as choke shorts, another body portion having an external cavityresonator formed therein and mounted over said window, a tuner mechanismin said external cavity resonator for tuning said reflex klystron, andmeans for suppressing undesired modes of operation of said reflexklystron comprising a wave trap coupled to said external cavityresonator through an opening in the wall of said external cavityresonator, said wave trap having a wave energy absorbing member thereinfor absorbing the energy of said undesired mode, the electrical lengthof said wave trap being of suflicient dimension to suppress theundesired mode of operation of the reflex klystron.

References Cited in the file of this patent UNITED STATES PATENTS2,591,696 Hansen Apr. 8, 1952 2,644,889 Finke et al. July 7, 19532,678,404 Sorg May 11, 1954 2,806,977 Carter Sept. 17, 1957 2,815,467Gardner Dec. 3, 1957 2,824,258 Snow et al Feb. 18, 1958 FOREIGN PATENTS1,108,985 France Sept. 14, 1955 UNITED STATES PATENT OFFICE CERTIFICATEOF CORRECTION Curtis E, Ward Column 1, line 21., column 2 line 59, forcolumn 4, lines 2 and 3, a main body portion havin for "kylstron" readklystron flexibiltiy" read flexibility strike out "resonator typecomprising g an evacuatedfl Signed and sealed this. 11th day of April1961a (SEAL) Attest:

ERNEST W SWIDER ARTHUR W. CRUCKER Attestmg Gfi'icer Acting Commissionerof Patents

